Vacuum forming apparatus for forming a three-dimensional surface article

ABSTRACT

A vacuum forming process and related apparatus are disclosed. The vacuum forming process and apparatus can be used for molding a thin sheet of thermoformable plastic into an accurate three-dimensional relief reproduction of an original artwork such that the plastic sheet carries a permanent image of the original work.

This application is a divisional of application Ser. No. 08/618,401,filed Mar. 19, 1996 and now U.S. Pat. No. 5,667,747, which is a FileWrapper Continuation of Ser. No. 08/408,900, filed Mar. 22, 1995 and nowabandoned.

FIELD OF THE INVENTION

This invention relates to a vacuum forming process and related apparatusfor molding a thin sheet of thermoformable plastic into an accuratethree-dimensional relief reproduction of an original artistic work wherethe plastic sheet carries a permanent image of the original work.

BACKGROUND OF THE INVENTION

Society's renewed interest in works of arts has resulted in the demandfor inexpensive reproductions of the original. For many years, societyhad to contend with two dimensional reproductions which were most oftenreproduced by a photographic process. These two dimensionalreproductions failed to reproduce what was often an essentialcharacteristic of the work, the relief. For some paintings, for example,part of the genius of the work not only lies in the image produced butin the texture of the work such as the brush stroke, which, for example,may reflect light in a particular manner.

One of the first obstacles to achieving this goal is the manner in whichthe third dimension of the art work can be reproduced. Various methodshave been set forth in order to recreate that third dimension, however,some of those methods involve making a matrix from the original workitself pouring a substance over the original work to copy its relief;(U.S. Pat. Nos. 4,285,744; 4,971,743; French Patents 1,493,516 and1,548,337). Unfortunately, this procedure is simply not acceptable whenreproducing originals as it may jeopardize the physical integrity of thework and with masterpieces they are simply not available for use.

From the matrix a female and possibly a male molding die is made. Thesedies constitute the molds against which the image carrying substratewill be pressed. The molding may be accomplished by a press, a vacuum orother devices which exert pressure on the substrate.

The problem encountered in pressing the substrate consists of finding amedium capable of adequately reflecting the definition sought. It hasbeen found that PVC is a medium which can be properly deformed undercontrolled conditions. Unfortunately, this material must be heated priorto pressing and this often leads to displacements and distortions of theimage contained on it.

Traditional processes have attempted to deal with the above problems inthe following manner. Canadian patent application 2,020,206 and its U.S.counterparts 5,182,063 and 5,201,548 put forth an alternative method forforming a matrix which reflects the three dimensional features of thework of art, without jeopardizing the original work. A similar approachis also described in U.S. Pat. No. 4,001,062. Two photographs of theoriginal work are taken, and are put side by side on a carrier. Thetransparent substrate, upon which the three dimensional elements will bereproduced, is placed over one of the images. An artist then beginsrecreating the relief (for instance, the brush strokes) by referring tothe image underneath the substrate. When it becomes difficult to see theimage beneath the substrate because it is covered with paste, then theartist may simply refer to the other image beside it. By having anartist reproduce the three dimensional elements of the original work ona matrix, and then forming the mold from that disposable matrix, theoriginal work of art is never touched. On the other hand, one of thedrawbacks of this procedure is that once the artist begins relying onthe image beside the substrate, and not the one underneath, faithfulreproduction of the relief becomes less accurate.

In order to ensure adequate definition during the pressing process, manyprior approaches (U.S. Pat. Nos. 4,971,743; 5,116,562 and 4,285,744)require that the image carrier, which is most often a sheet of PVC, beheated to its softened state immediately prior to embossing. The PVC isusually heated to 110° C. to 130° C. As it is softened, the sheet of PVCbows over the female embossing die but does not come into contact withit. The press is then elevated so that the softened PVC fills all thenotches and indentations of the die, and the pressure is then appliedfor the necessary amount of time. Unfortunately, the heating of thesheet of PVC to its softened state inevitably results in unequalsoftening, so that some sections of the PVC will soften more quicklythan others and consequently, they will bow before others, which resultsin the displacement of the image. Therefore, the molded relief does notcorrespond with the image. In the process of U.S. Pat. No. 5,182,063,canvas is impregnated with a resinous material to form a substrate. ThePVC sheet material with image is then melted and pressed against thesubstrate to bond the PVC sheet to the substrate. The pressing operationinvolves the use of dies which press the desired relieve into the PVCand substrate sandwich. Although the image appears to be stable onsubstrate, additional processing is required to ensure such stability.

For this reason, some inventions, such as U.S. Pat. No. 4,285,744,provide a means for molding a PVC substrate, while upholding the qualityof the image, by heating it quickly to its softened state, by monitoringthe distribution of the heat, and by subsequently cooling it rapidly. Inother words, attempting to reduce the amount of time during which thePVC bows over the die. However, in light of the inherent structure ofPVC, it is impossible to predict the manner in which it will soften,even if the heat is regulated.

The present invention in accordance with one aspect seeks to overcomethe shortcomings of the prior art in the following manner. Whenrecreating the three dimensional qualities of the original work of arton a matrix, this invention ensures that the image on the substrateremains visible at all times so that the artist does not have to make acalculated guess as to the placement of a particular relief. This isaccomplished by projecting the image onto the substrate, either throughthe use of a standard photography lens enlarger or its equivalent. Byprojecting the image, the artist is always able to see the workregardless of the amount of paste covering the substrate which equallyincreases the reliability of the three dimensional reproduction.

Furthermore, prior to the pressing process, this invention does notrequire that the PVC be heated to such an extent that the sheet droopsover the die, thus increasing the likelihood of distortion ordisplacement of the image in relation to the relief. Instead, theplastic sheet is heated to a first temperature immediately prior tomolding and the temperature is increased further once the pressure ofthe vacuum is applied. In other words, the optimal temperature requiredfor forming the plastic sheet is still achieved, however, this finalsoftened state is achieved only once the plastic sheet is contained inthe mold, at which point there does not remain any possibility ofdistortion or displacement of the image in relation to the relief.

The present invention uses vacuum as opposed to opposing presses, inorder to apply the required pressure for molding the PVC. Although avacuum forming machine may be less effective than opposing pressing ofmatting dies such as described in U.S. Pat. No. 4,285,744, thisinvention overcomes most of the shortcomings by allowing for thedrilling of a multitude of minuscule holes into the female die, whichwill result in the increased effectiveness of the suction of the vacuumon the image carrier substrate, and consequently, this will result inincreased definition of the relief embossed. Although U.S. Pat. No.4,308,224 describes the use of microscopically small air channels in thedie, they are for a completely different purpose to allow air to escapeduring the melting of the foil. The foil in its molten state takes onthe shape of the mold as the molten foil flows into the mold and movesair out from beneath the foil through the air channels.

Although the process in accordance with this invention may not result ina three-dimensional reproduction that is as high quality as some of theother procedures, the method provides for a significant reduction in theproduction time.

SUMMARY OF THE INVENTION

In accordance with an aspect of the invention, a vacuum forming processfor molding a thin sheet of thermoformable plastic, and an accuratethree-dimensional relief reproduction of an original artwork, the sheetof plastic having printed on one side thereof a permanent image of theoriginal artwork, the process comprises:

i) supporting the printed sheet of plastic proximate a vacuum formingfemale mold with the printed side facing the mold, the female moldhaving a surface relief therein which is a reproduction of the surfacerelief of the original artwork, the image being in register with thesurface relief of the mold, a multitude of vacuum forming holes beingprovided in the mold;

ii) heating said plastic sheet;

iii) contacting the mold with the sheet once the sheet is heated to afirst temperature which is below normal thermoforming temperatures wherethe first temperature minimizes movement of the image relative to themold due to heating of the sheet, immediately applying a vacuum to theholes in the mold to commence drawing the plastic sheet into the moldand fix thereby the sheet relative to the mold relief to furtherminimize image movement, on the sheet relative to the mold;

iv) continuing to heat the plastic sheet while maintaining vacuum on theholes in the mold to complete forming of the three-dimensional relief inthe sheet;

v) stop heating the plastic sheet once it has attained a secondtemperature in the range of normal thermoforming temperatures whilecontinuing to apply vacuum to the mold holes, applying cooling to thesheet after heating is stopped to cool the sheet below the firsttemperature to a third temperature to render permanent thethree-dimensional relief formed in the sheet,

vi) stop cooling the sheet and remove the sheet from the mold.

In accordance with another aspect of the invention, an apparatus forvacuum forming a thin sheet of thermoformable plastic into an accuratethree-dimensional relief reproduction of an original artwork, the sheetof plastic having printed on one side thereof a permanent image of theoriginal artwork, the apparatus comprising:

i) a vacuum forming female mold having a surface relief therein which isa reproduction of the surface relief of the original artwork, amultitude of vacuum forming holes being provided in the mold;

ii) means for supporting the printed sheet of plastic proximate the moldwith the printed side facing the mold, the support means supporting theimage in register with the surface relief of the mold;

iii) means for heating the plastic sheet, the heating means beingmounted on means for reciprocally moving the heating means from a firstposition away from the mold to a second position over and spaced fromthe unprinted side of the plastic sheet;

iv) means for relatively moving the plastic sheet and the mold tocontact the plastic sheet with mold when the heating means in the secondposition heats the plastic sheet to a first temperature which is belownormal thermoforming temperatures;

v) means for sealing a perimeter of the plastic sheet to a correspondingperimeter of the mold;

vi) means for applying a vacuum to the multitude of holes in the moldwhen the sealing means seals the plastic sheet and the plastic sheet isat the first temperature;

vii) the reciprocating means moving the heating means back to the secondposition when the plastic sheet is at a second thermoformingtemperature;

viii) means for cooling the plastic sheet with the heating means in thesecond position;

ix) means for removing the vacuum from the multitude of holes when theplastic sheet is cooled by the cooling means to a third temperature, thesealing means releasing a seal between the mold and the plastic sheet topermit removal of the formed plastic sheet from the mold.

In accordance with another aspect of the invention, a method ofproducing a male mold for use in making a female mold which is used invacuum forming a thermoformable plastic sheet to form an accuratethree-dimensional relief reproduction of an original artwork, comprises:

i) mounting a substrate sheet;

ii) projecting an image of the original artwork onto the substratesheet;

iii) applying a moldable compound to the substrate to replicate brushstrokes of the original image where projection of the image onto thesubstrate guides application of the compound; and

iv) allowing the compound to harden to provide the mold from which afemale mold is made.

In accordance with another aspect of the invention, a method is providedfor producing a male mold for use in making a female mold which is usedin vacuum forming a thermoformable plastic sheet to form an accuratethree-dimensional relief reproduction of an original artwork, the methodcomprises:

i) thermoforming a canvas relief in a thermoformable plastic sheet whichhas an image of the original artwork printed thereon;

ii) applying a moldable compound to the printed surface of the sheet toreplicate over the image brush strokes of the original image, theprinted image guiding application of the compound; and

iii) allowing the compound to harden to provide the male mold from whicha female mold may be made.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the invention are described with respect to thedrawings wherein:

FIG. 1 is a perspective view of an image projection system forprojecting an image onto a substrate;

FIG. 2 is a perspective view of the application of a moldable compoundto the substrate to replicate the brush strokes of the original;

FIG. 3 is a perspective view of the formed male mold to be mounted on asolid backing;

FIG. 4 is a section along the section lines of FIG. 3;

FIG. 5 demonstrates pouring of a curable material from which the femalemold is made;

FIG. 6 is a section through the male and female molds as contained in amolding box;

FIG. 7 is a section through the female mold;

FIG. 8 illustrates the drilling of a multitude of holes in the femalemold;

FIG. 9 is a perspective view with a portion thereof removed toillustrate details thereof;

FIG. 10 is an enlarged section of the female mold showing the relativeminuscule size holes provided in the relief surface;

FIG. 11 is a perspective view showing the mounting of the female mold inthe vacuum box of the vacuum forming machine;

FIG. 12 is a section showing the support of the thin plastic sheet abovethe female mold and the relative positioning of the heating device;

FIG. 13 shows the movement of the vacuum box upwardly to seal againstthe heated thermoformable sheet with the application of vacuum to form arelief in the sheet;

FIG. 14 is a perspective view of the vacuum forming machine;

FIGS. 15A, 15B and 15C illustrate in sequence the application of heatand drawing of a vacuum on the sheet;

FIG. 16 is a top view of the sheet showing the temperatures of the sheetbefore the vacuum is applied in FIG. 15C;

FIGS. 17A, 17B and 17C illustrate the sequence of events where heatingis removed, vacuum is continued and cooling is applied to thethermoformed sheet;

FIG. 18 is a top view showing the temperatures of the sheet at the timeof removal of the heating means, as shown in FIG. 17A;

FIG. 19 is a view of the thin plastic sheet having an image printedthereon;

FIG. 20 shows the vacuum forming a canvas relief into the printedplastic sheet of FIG. 19;

FIG. 21 is an enlarged view showing the canvas mounted on the vacuum boxover which the sheet of FIG. 19 is placed in the vacuum former of FIG.20;

FIG. 22 shows the plastic sheet having the canvas relief thermoformedtherein;

FIG. 23 illustrates the application to the sheet of FIG. 22 of amoldable compound to replicate on the surface the brush strokes of theoriginal;

FIG. 24 illustrates the application of a curable compound for formingthe female mold from the male mold of FIG. 23; and

FIG. 25 is a section through the mold box of FIG. 24 with the femalemold being formed on top of the male mold of FIG. 23.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The vacuum forming process in accordance with this invention greatlyexpedites production time in producing a printed image on a plasticsheet which has formed therein an accurate three-dimensional reliefreproduction of the original artwork where the relief is in registerwith the image. The process and apparatus of this invention may beapplied in making a variety of art reproduction for use in severaldifferent fields. The conventional use is to form art reproductionswhich may have canvas backing, masonite backing or chipboard backingwhere the reproduction once framed appears to be essentially identicalto the original. Such art reproduction may also be used in the apparelindustry where the artwork of different shapes and sizes, as produced bythis invention, can be attached to garments in the form of sheets,vests, jackets, jeans and caps. The vacuum formed material can also belaminated to sport bags, duffel bags, baseballs, footballs, soccer ballsand other sport items. In the packaging industry, the vacuum formedimages in accordance with this invention, may be applied to productpackages such as packaged foods, fragrances, clothing and apparelpackages and the like. Such packages can then have a surface texture ofartwork which enhances the marketing of the product. Other fields of usefor the invention include the application of the vacuum formed artworkon puzzles, paint by number artwork, board games, maps and the like.

Although techniques have been described for forming the male and femalemolds from the original artwork, as previously discussed, this cangreatly damage the original artwork which can result in either having todispose of the original artwork or require extensive touch ups by theartist. In accordance with an aspect of this invention, as describedwith respect to FIGS. 1 through 7, a female mold may be made for thevacuum forming process and apparatus which does not require contactingthe original artwork with any form of molding material. As shown in FIG.1, a substrate 10 is mounted on a solid support 12. The substrate 10, inaccordance with this embodiment, comprises a canvas sheet 14 mounted ona solid backing 16. The solid backing may be masonite, chipboard orother substantially rigid planer material. A projection system 18 isspaced from the substrate 10. The image projection system includes aslide 20 which is the positive of a negative exposure of the originalartwork. Such positive is developed in the normal film processingtechnique where the original is photographed with a camera, usually acamera using the 4 inch by 5 inch standard format. The image on theslide 20 is projected towards the substrate 10 by a projection lamp 22.The image is focused on the substrate 10 by the usual focusing lens 24on the projector 18. The image once focused appears as a scene depictedby a mountainous topography 26 on the canvas 14. It is understood thatthe projection of the image may be horizontal to allow one to work on avertical surface or the projection may be vertical to allow one to workon a horizonal surface. The objective is to now reproduce over the imageand on top of the canvas the brush strokes similar to those of theoriginal artist.

As shown in FIG. 2, the brush strokes may be replicated on the canvas byusing the image 26 as a guide. A moldable compound is applied to thecanvas by use of a brush 28 and/or a spatula 30. The person applying thecompound has artistic ability and is able to interpret the originalartwork as shown by the image to apply a surface texture on the canvaswhich replicates the brush strokes and sculpting of the original artist.There are several moldable compounds available to achieve thisobjective. For example, as supplied in the container 32 a moldablecompound of acrylic polymer molding paste and/or acrylic polymer gel maybe used. The operator slowly builds up on the substrate surface themoldable compound to replicate the brush strokes and sculpting.Continuous projection of the image onto the canvas surface 14 allows theoperator to perfect the brush stroke replication over an extended periodwhere the projected image acts as a guide to ensure that the strokes areproperly applied to reproduce as accurately as possible the surfacetexture in relief of the original artwork.

To assist the artist in reproducing the brush strokes the moldablematerial may be opaque and of a white color to enhance and delineate thereproduced work. By using a white material the image as projectedcontinues to show up clearly on the areas that have been covered withthe compound.

As shown in FIG. 3, the completed brush stroke reproduction 34 ismounted on a solid base 36. The solid base may be three quarters of aninch plywood or other rigid material. As shown in FIG. 4, the canvas 14has on its surface the hardened molding compound 38. In section, therelief of the hardened compound 38 replicates the brush strokes andsculpting of the original artwork. The hardened compound 38 therebyforms on the canvas backing 16, as mounted on the plywood 36, a malemold from which a female mold may be made.

As shown in FIG. 5, a frame 40 may be secured to the base 36 to provideupright sides 42 and ends 44. A curable resin 46 is then poured from acontainer 48 to cover the male mold 34. The resin 46 in its uncuredstate immediately takes on the surface relief of the male mold 34, asdefined by the hardened compound 38. Sufficient resin poured from thecontainer 48 to completely cover the male mold 34 and to a level in theframed mold to provide a female mold of a thickness in the range of 1/4inch to 3/4 of an inch in thickness. The section of FIG. 6 shows thefemale mold 50 having a level backwall 52 and contained within the frame40. The male mold, as provided in the frame 40, has the backing 36, thesolid substrate 16 and the canvas layer 14. Preferably, the hardenedcompound 38 is coated with a suitable release agent to permit easyremoval of the female mold 50 from the frame 40. The poured resin 46 iscured in accordance with standard practice for the selected resin. Forexample, a preferred resin is an epoxy resin having up to 80% by weightof aluminum as a heat conductive filler. The resin is cured by cyclicalheating for 20 minutes on and then 20 minutes off. A preferred epoxyresin may be obtained from Chemque of Quebec and sold under thetrademark Chemcast 402. Once the resin is properly cured to a hardenedstate the frame 40 is removed and the mold 50 lifted away from the malemold 34. This provides in section the female mold 50 free of the malemold and carrying on its surface indentations 54 in relief which inessence is the negative of the positive image of the original brushstrokes.

As shown in FIG. 8, the female mold 50 has drilled through its section amultitude of minuscule holes. The holes may be formed by using a drill56 with a drill bit 58. The drill bit is preferably of 1/32" to 1/64" indiameter or less. The number of holes drilled through the female mold 50will vary depending upon the surface texture of the female mold.Normally the holes are drilled every 1/2 inch to provide in the range of9 holes per square inch of female mold surface. Care is taken indrilling the holes considering the fragile nature thereof not to chipthe mold surface and also to judiciously locate the holes in the surfacein the manner shown with respect to FIG. 10. The enlarged section of thefemale mold 50 shows a number of cuts 60 or rifts 62 in the surface.Holes are therefore not only drilled in the more planer portions 64 butas well, careful steps are taken to ensure that the fine holes are alsoprovided in the cuts or rifts 60 and 62. As shown in FIG. 10, the veryfine minuscule holes extend through the body 66 of the female mold tothe backside 52 thereof. An exemplary hole is shown through the body 66at 68.

The female mold is then of a size corresponding to the size of theartwork to be reproduced. A vacuum forming box 70, as shown in FIG. 9,is provided with a cooling coil 72. The female mold 50 is inserted inthe vacuum forming box 70 and rested on the interior ledge 74 such thatthe uppermost surfaces of the female mold 50 are below the upperoutermost perimeter edge 76 of the mold box. The cooling coil 72 has asuitable coolant introduced through inlet 78 and discharged from thecoil through outlet 80. Cooling water, gaseous refrigerant or the likemay be used depending upon the extent of cooling required. The coolingcoil is positioned in the vacuum forming box 70 so as to be immediatelybeneath and preferably in contact with the underside of the female mold50. This ensures optimum cooling of the mold as required, particularlywhen the mold is used on a continuous basis and in vacuum forming theart reproductions. To facilitate vacuum forming, a vacuum is drawnthrough conduit 82, enters a plenum beneath the female mold 50 asdefined by interior partition 84. The vacuum conduit 82 is incommunication with the plenum, as defined by partition 84 through anenlarged inlet 86. With the female mold 50 secured in the vacuum box 70on top of ledge 74, a seal is provided about the perimeter of the mold50 so that vacuum, as drawn in the plenum above partition 84 holds avacuum on the hole 68 which are in communication with the surface of thefemale mold.

The vacuum box 70, as shown in FIG. 11 is assembled and is ready toreceive the thermoformable plastic sheet 88 which has an image 26printed thereon which is identical to the image 26 projected onto thesubstrate 10 of FIG. 1. The objective is to now thermoform in theplastic sheet 88 the surface relief so as to replicate the brush strokesof the original. As is appreciated by those skilled in the art, thereare a variety of thermoformable plastics available which may be used inthe vacuum forming process. The preferred thickness of the sheets is inthe range of 10 to 12 mil. Preferred plastic materials includecopolymers of polyvinylchloride where the surface of the plastic sheetmay be treated so as to receive the printed image and permanently retainthe image on its surface. Titanium dioxide and the like may also beincluded in the plastic material to give the material somewhat of apaper feel as well as provide a suitable base on which printing may beapplied. The printing of the sheet may be carried out in accordance withany of the well known printing techniques, where the image as printed onthe sheet is essentially identical in color and definition as found inthe original.

The sheet 88 is positioned over the vacuum box 70 with the image 26facing towards the female mold 50. Although it might be possible toposition the sheet 88 over the female mold where the image 26 is inregister with the recesses cuts and grooves in the surface of the mold,it is best to ensure registration by use of suitable guides. As shown inFIG. 12, corner guides 90 are provided at the corners and are of aspacing to correspond to the dimensional spacing of the corners 92 ofthe printed sheet 88. This ensures that the definition of the coloredimage on the sheet 88 is in register with the recesses of the femalemold 50 such that when the sheet is thermoformed the relief provided onthe sheet 88 is in register with the image, hence, when thethermoforming of the sheet is complete the overall effect is essentiallythe same as the original in replicating the brush strokes and sculptingof the original artwork.

In order to effect thermoforming of the sheet 88, it is supportedslightly above the female mold 50 in the mold box 70. By slightly aboveit is intended that the sheet 88 is proximate the relatively cool femalemold 50 but is spaced slightly therefrom to facilitate rapid heating ofthe sheet surface. The mold is supported by way of opposing clampmembers 94 and 96. The clamp member 96 has a raised ledge portion 90about its perimeter where the edge portion 90 is identical to the edgedimension in 92 of the plastic sheet 88. This ensures, with properpositioning of the clamp member 96, that the image on the underside ofthe sheet 88 is in register with the relief of the mold 50. Clampmembers 94 then clamp the sheet 88 against the bottom clamp members 96.

A heating device 98 is brought over top of the sheet 88. The heatingdevice may be mounted by way of rollers 100 on tracks 102 to allowreciprocal movement of the heating device over and away from the sheet88. The heating device 98 may include heating elements 104 which areelectrically powered to radiate the sheet 88 with infrared radiation.Such heating of the sheet is controlled in a manner in respect of thesequence of events described in reference to FIGS. 15, 16, 17 and 18. Inany event, the heating of the sheet 88 does not cause it to drop ontothe female mold 70 but instead to soften it to a point where it is aboutto droop towards or onto the mold 50.

As shown in FIG. 13, during continued heating of the sheet 88, the moldbox 70 is elevated in the direction of arrow 106 where the mold boxincludes a raised outermost perimeter edge 76 which contacts the sheet88 about its corresponding outer perimeter edge 88A. At this time vacuumis applied to conduit 82 to draw a vacuum on the holes 68. The sheet isat a sufficient temperature such that the vacuum pulls the sheet 88downwardly onto the relief surface 108 of the female mold 50. Due to thecontact between the upper edge of the vacuum box periphery 78 with thesheet in region 88A, a seal is formed between the vacuum box and thesheet. Hence, vacuum drawn through hole 68 draws the sheet downwardlybecause no air enters between the sheet and the mold face 108. Whilevacuum continues to be drawn, the heating device 98 remains over thesheet 88 continuing to heat it with infrared radiation 110. As will bediscussed with respect to the cycle of events of FIG. 17, the heat iseventually withdrawn, vacuum maintained, cooling of the sheet effectedand then release of the sheet by opening of the clamps 94 and 96 so thatthe sheet may be removed from the vacuum forming box.

Although it is understood that a variety of vacuum forming machines areavailable in which the vacuum forming box of this invention may beemployed, a preferred apparatus is shown in FIG. 14. The vacuum formingapparatus 112 comprises a support base 114 on which a solid table 116 ismounted. Hydraulic cylinders 118 are used to raise and lower the solidtable 116, the movement being guided by guides 120. The support for theplastic sheet is in the form of clamps 94 and 96 which are pivotallyconnected to a hinge mechanism at 122. The hinge mechanism 122 issecured to the base 114. The clamps are moved toward and away from oneanother by hydraulic cylinders 124 where the lower clamp 96 includes thelip area 90 to register the sheet 88 over the female mold 50 which ishoused in the mold box 70. The interior perimeter of the clamp 96 isgreater than the exterior perimeter of the mold box 70, as shown in FIG.13. The spacing between the outermost perimeter of the mold box, asdefined by edge 76 is within the inside 97 of the lower clamp 96. Inoperation the print is placed in the lower clamp 96 and the upper clamp94 pressed against the lower clamp by actuation of the hydrauliccylinders 124. The heating device 98 on rails 102 is moved over top ofthe sheet secured in the clamps. When the sheet is heated to the desiredtemperature, the mold box 70 is moved upwardly within the clamp 96 byway of extension of the hydraulic cylinders 118. This effects, aspreviously described, the seal between the mold box and the sheet 88.

After completion of forming of the sheet 88, the heating device 98 isretracted to its first position, as shown in FIG. 14, which then clearsthe area such that cooling fans 126, as mounted on crossbar 128 areactuated to direct cooling air down onto the sheet 88. The sheet 88 isthen cooled to the appropriate temperature to stabilize sheet integrityso that it remains flat and essentially wrap free and render the moldedrelief in the sheet 88 permanent. At that time clamps 94 and 96 areopened to allow removal of the sheet from the mold box 70.

Cooling of the female mold 50 is preferably conducted on a continuousbasis. Refrigerant is circulated through the coil 72 to continuouslycool the mold 50. Such cooling greatly decreases the cycle time of thevacuum forming machine 112 because the surface temperature of the mold50 should be kept below the temperature to which the sheet 88 is cooledbefore removal from the mold. It is understood however that cooling ofthe mold 50 may not be required when the cycle times of the machine aregreatly increased. This provides sufficient time for the mold to cooldown after each cycle before heat is subsequently applied again to thesheet in the next cycle.

The cycle times for the machine are described with respect to FIGS. 15through 18. In FIG. 15A the sheet 88 is clamped above the vacuum box 70with the heater 98 in its first position. This is the commencement ofthe cycle. With the sheet 88 spaced slightly above the vacuum box 70,the heater 98 moves to its second position, as shown in FIG. 15B. Oncethe heater is located in its second position, this indicates the zerotime of the cycle. Heat is applied to the sheet 88 until it attains afirst temperature which is below normal thermoforming temperatures forthe selected thermoformable plastic. Once this first temperature isattained the vacuum box 70 is moved upwardly in the direction of arrow106 and a vacuum is drawn through conduit 82. This places the sheet 88against the female mold in a manner described with respect to FIG. 13.The temperatures for the sheet are illustrated in FIG. 16. Thermocoupleswere located on the sheet to determine its surface temperature at thetime when the vacuum was drawn and also to provide an average value forthe first temperature. As shown in FIG. 16, the temperatures over thesurface of the sheet are fairly consistent ranging from 203° F. up to210° F. (95° C.-100° C.). The preferred range is therefore about 90° C.to 100° C. which is acceptable considering the type of heating deviceused as well as the space between the heating device 98 and the sheet88. At this temperature the sheet is not considered to be at itsthermoformable temperature, however, it is sufficiently pliable thatwhen vacuum is drawn the sheet moves downwardly onto the surface of themold. However, the sheet still has sufficient structural integrity thatit does not confirm exactly to the mold surface in terms of taking onthe shape of all the cuts and crevices of the mold. At this temperaturethe printed image on the underside of the sheet has not moved relativeto the relief on the mold surface, hence the image continues to bealigned with the relief on the mold surface. As is generally understood,as the plastic is heated, normally the plastic begins to move due toirregularities in the physical properties across the sheet length andalso due to the memory of the sheet with respect to strain and stress.It has therefore been discovered that in drawing a vacuum on the sheetbefore the image begins to move about on the sheet, registry of theimage with the mold relief can be maintained and distortion in the imageof the final product can be minimized or essentially eliminated.

Vacuum is continued on the vacuum box 70 through the conduit 82 with thesheet 88 being against the face of the mold surface. As heating of thesheet continues its temperature is elevated to normal thermoformingtemperatures which allows the sheet to then move into all of the cuts,crevices and other relief depressions in the female mold, therebycompleting the formation of the desired relief in the sheet surface onthe printed side. It has been found that vacuum applied to conduit 82 iswithin the normal range of approximately 20 pounds per square inch whichprovides for an external pressure on the sheet 88 equivalent toatmospheric pressure of 14.7 pounds per square inch. When the sheet hasachieved a second temperature which is within the normal thermoformingtemperature ranges, the heating device 98 is retracted to the firstposition while vacuum is maintained on the vacuum box 70. As shown inFIG. 18, the temperature of the sheet at the time of retracting of theheating device 98 is approximately in the range of 310 to 323° F. (155°C.-160° C.). Again, the discrepancies in temperatures across the sheetare due to the type of heating device used as well as the space inbetween the heating device and the sheet, air currents and the likewhich can cause regional cooling of the sheet. The preferred secondtemperature for the sheet is then in the range of 150° C. to 170° C.which is considered to be in the upper range of normal thermoformingtemperatures for the selected polyvinylchloride copolymer sheet.

With the heating device 98 in its second position, the surface of thesheet 88 is exposed, as shown in FIGS. 17B with vacuum continued to beapplied. As shown in FIG. 17C, cooling fans 126 are actuated to directcooling air in the direction arrows 128 onto the surface of the sheet.As already noted, the vacuum box 70 includes cooling coils to ensurethat the temperature of the female mold is below the third desiredtemperature at which the relief thermoformed in the plastic sheetbecomes permanent. Preferably, the third temperature for the selectedpolyvinylchloride copolymer sheet is in the range of 120° F. (50° C.) orless.

It is possible to control the sequence of events for the vacuum formingmachine by measuring temperature of the surface of the sheet 88. It hasbeen found that due to the consistency in the physical characteristicsof the sheet 88, it is possible to operate the vacuum forming machine112 on the basis of cycle times. For the selected polyvinylchloridecopolymer sheet, it has been found that ideal processing times for thetype of heating device used is heating of the sheet to the firsttemperature in 10 to 12 seconds. Application of the vacuum fromapproximately 12 seconds to 25 seconds. The heater is then withdrawn andmoved to its first position after 25 seconds from the commencement.Vacuum is continued to be applied and cooling directed onto the sheetfor a further 20 to 25 seconds at which point after a total of 32 to 50seconds, the clamps are released and the sheet is removed. Consideringapproximately 15 seconds setup time and locating the sheet in themachine and approximately 15 seconds for removing the sheet from themachine, a total cycle time of approximately 1 to 1.5 minutes isprovided. It is appreciated though that the vacuum forming machine maybe automated to further reduce the cycle time. This cycle time isconsiderably less than the cycle time of other plastic thermoformingmachines in making artistic reproductions. Normal cycle times for mostprior art machines are in the range of 5 to 6 minutes. Hence, by way ofthe method and apparatus of this invention, the cycle time isconsiderably reduced to realize a significant economy in productionwhile continuing to produce an acceptable product for various marketsegments.

Although the vacuum may remain applied to the vacuum box until the endof cooling, it has been found that with most applications with PVCsheet, that the vacuum can be removed from the vacuum box atapproximately 45 seconds from startup because with appropriate coolingdevices, the sheet is cooled to a sufficiently reduced temperature thatthe relief as thermoformed in the sheet remains in its defined pattern.However, if there are difficulties in that respect it is desirable tomaintain the vacuum on until the end of the cooling cycle and thetemperature has reduced to an acceptable level in the range of 120° F.or less.

As an alternative embodiment to the procedure described in respect ofFIGS. 1 through 6, FIGS. 19 through 25 set out another procedure formaking the male mold. As shown in FIG. 19, a plastic sheet 130 which maybe of PVC material has an image 132 printed thereon. The sheet issubstantially flat and smooth and in essence is the same as sheet 88used in respect of the thermoforming process described in FIG. 11. Inorder to modify the sheet 130 to resemble an original piece of art, acanvas relief is formed into the surface. This is accomplished byclamping the sheet 130 in the clamps 96 and 98 above a vacuum box 70. Acanvas 134 is laid over the vacuum box 70 where the perimeter edge 76 ofthe vacuum box elevates the edge portion 136 of the canvas sheet. Withthe vacuum box 70 elevated against the plastic sheet 130, the heatingdevice 98 applies heat to the sheet 130. Vacuum is applied to theconduit 82 to draw the sheet 130 down onto the canvas 134 where a sealis formed in the region 138 as the sheet is pushed against the edge 76with the canvas 134 sandwiched therebetween. Heating and vacuum iscontinued until the matrix of the canvas is formed in relief on theplastic sheet 130. The heating process is conducted in a manner toensure that the image 132 is not distorted so that the sheet as cooledand removed from the vacuum forming mold resembles the sheet 140 asshown in FIG. 22 where a canvas matrix 142 is on the surface of thesheet having the image 132. In order to replicate the brush strokes onthe thermoformed sheet 140, an artist uses a molding compound which isapplied to the image in a manner to reproduce the brush strokes of theoriginal. Preferably the molding compound as applied to the surface ofthe sheet 140 is clear so that the image 132 continues to be visiblebeneath the molding compound. A suitable molding compound which isuseful in this regard is the clear acrylic polymer gel used by artistsfor certain acrylic artistic works. The molding compound, as supplied incontainer 144, is applied by a brush 146 or pallet knives, sponges,dabbing clothes or tissues as commonly employed by artists. The clearmolding compound is allowed to harden and then constitute the male moldfor forming the female mold. As with the first embodiment of FIG. 5 and6, a curable resin 46 is poured onto the male mold surface 148 from thecontainer 48. The male mold 148 is supported on a plywood backing or thelike, as was done with respect to the embodiment of FIG. 3, andsurrounded by a suitable frame 40. The curable resin 46 is poured intothe mold box and contained by the frame 40 to a level shown in FIG. 25.The resin 46 is then cured to form a female mold body 150 having asmooth rear face 152 and a three-dimensional relief face 154 which isthe female mold replica of the male mold surface 148. As with the firstembodiment, the male mold surface may be treated with a release materialsuch as a silicone. After the resin is cured to form a hard female moldbody 150, the mold is broken open and the female mold released from themale mold 148. The female mold is now ready for treatment in accordancewith the embodiments of FIGS. 7 and 8 before installation in the vacuumbox 70. In accordance with the second embodiment for forming the femalemold, a direct approach in providing the brush strokes on the surface byuse of the molding compound is achieved. Assuming that the selectedmaterial for the sheet 130 is readily thermoformable, the canvas matrixis readily provided in the sheet. However, for selected materials orthicker materials which are desired in making the male mold, the firstembodiment is preferable in that the artist reproduces the brush strokesdirectly on the canvas material.

In accordance with this invention, a consistent quality product isproduced which forms a faithful reproduction of the original artisticwork. Products made by the process and apparatus of this invention havemany end uses as previously discussed and are not only limited toreproduction of original works which are framed.

Although preferred embodiments of the invention are described herein indetail, it will be understood by those skilled in the art thatvariations may be made thereto without departing from the spirit of theinvention or the scope of the appended claims.

We claim:
 1. An apparatus for vacuum forming a thin sheet ofthermoformable plastic into an accurate three-dimensional reliefreproduction of an original artwork, the sheet of plastic having printedon one side thereof a permanent image of said original artwork, saidapparatus comprising:i) a vacuum forming female mold having a surfacerelief therein which is a reproduction of the surface relief of theoriginal artwork, a multitude of vacuum forming holes being provided insaid mold; ii) means for supporting the printed sheet of plasticproximate said mold with the printed side facing said mold, said supportmeans supporting the image in register with said surface relief of saidmold; iii) means for heating the plastic sheet, said heating means beingmounted on means for reciprocally moving said heating means from a firstposition away from said mold to a second position over and spaced fromthe unprinted side of the plastic sheet; iv) means for moving theplastic sheet and said mold relative to one another to contact theplastic sheet with said mold when said heating means in said secondposition heats the plastic sheet to a first temperature which is belownormal thermoforming temperatures; v) means for sealing a perimeter ofthe plastic sheet to a corresponding perimeter of said mold; vi) meansfor applying a vacuum to said multitude of holes in said mold when saidsealing means seals the plastic sheet and the plastic sheet is at thefirst temperature; vii) said reciprocating means moving said heatingmeans back to said second position when the plastic sheet is at a secondthermoforming temperature; viii) means for cooling the plastic sheetwith said heating means in said second position; ix) means for removingsaid vacuum from said multitude of holes when the plastic sheet iscooled by said cooling means to a third temperature, said sealing meansreleasing a seal between said mold and the plastic sheet to permitremoval of the formed plastic sheet from the mold.
 2. An apparatus ofclaim 1 wherein means is provided for cooling said mold to maintain saidmold at a temperature below the third temperature.
 3. An apparatus ofclaim 2 wherein a cooling coil is provided in contact with said moldbeneath said surface relief.
 4. An apparatus of claim 3, wherein saidmultitude of holes is each 1/32" in diameter or less, means enclosingsaid holes to provide a plenum behind said mold, said vacuum being incommunication with said plenum.
 5. An apparatus of claim 1 wherein saidsupport means includes a clamp for clamping the perimeter of the plasticsheet, said perimeter of said mold being dimensionally within an innerperimeter of said clamp.
 6. An apparatus of claim 5, wherein saidrelative movement means moves said mold toward the plastic sheet andsaid sealing means seals a perimeter portion of the plastic sheet withinsaid clamp, to said corresponding perimeter of said mold.
 7. Anapparatus of claim 1, wherein said heating means comprises a heatingelement for radiant heating of the plastic sheet.
 8. An apparatus ofclaim 1, wherein said cooling means comprises a cooling fan fordirecting cooling air onto the plastic sheet when said reciprocal movingmeans moves said heating means back to said first position.
 9. Anapparatus of claim 1 wherein a controller controls the timing ofactuation of said reciprocal moving means, said relative movement means,said sealing means, means for applying vacuum and means for removingvacuum during the vacuum forming to mold a relief in the plastic sheet.10. An apparatus of claim 1 wherein means is provided for registeringthe image with said surface relief of said mold.